U.S. patent application number 16/703406 was filed with the patent office on 2020-04-09 for ultrasound transducer and method for wafer level back face attachment.
The applicant listed for this patent is General Electric Healthcare. Invention is credited to Jason Barrett, Edouard Da Cruz, Flavien Daloz, Jean Pierre Malacrida.
Application Number | 20200107814 16/703406 |
Document ID | / |
Family ID | 62562703 |
Filed Date | 2020-04-09 |
United States Patent
Application |
20200107814 |
Kind Code |
A1 |
Daloz; Flavien ; et
al. |
April 9, 2020 |
ULTRASOUND TRANSDUCER AND METHOD FOR WAFER LEVEL BACK FACE
ATTACHMENT
Abstract
Methods and systems are provided for a single element ultrasound
transducer. In one embodiment, the ultrasound transducer comprises
a front face, a back face parallel to the front face, a
piezoelectric layer having a top surface electrically coupled to
the signal pad and a bottom surface electrically coupled to the
ground pad. In this way, the transducer can work robustly and may
be automatically mounted to an imaging probe.
Inventors: |
Daloz; Flavien; (Antibes,
FR) ; Barrett; Jason; (Queen Creek, AZ) ; Da
Cruz; Edouard; (Nice, FR) ; Malacrida; Jean
Pierre; (Saint Laurent, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
General Electric Healthcare |
Schenectady |
NY |
US |
|
|
Family ID: |
62562703 |
Appl. No.: |
16/703406 |
Filed: |
December 4, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15385671 |
Dec 20, 2016 |
10561398 |
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16703406 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B06B 1/0644 20130101;
H01L 41/338 20130101; A61B 8/4483 20130101; H01L 41/313 20130101;
H01L 41/0815 20130101 |
International
Class: |
A61B 8/00 20060101
A61B008/00; B06B 1/06 20060101 B06B001/06; H01L 41/313 20060101
H01L041/313; H01L 41/08 20060101 H01L041/08; H01L 41/338 20060101
H01L041/338 |
Claims
1-20. (canceled)
21. A method, comprising: laminating a first comb structure and a
second comb structure into an acoustic stack, the first comb
structure having fins including a piezoelectric layer intermediate
a matching layer and a backing layer, the second comb structure
having fins and kerfs; plating a first conductive layer over a top
surface of the acoustic stack; plating a second conductive layer
over a bottom surface of the acoustic stack; cutting a groove
through the second conductive layer; dicing the cut acoustic stack
into an ultrasound transducer having a back face including a signal
pad and a ground pad formed by the second conductive layer and
separated by the groove; and inserting a distal end of a flex
attachment into the groove, the flex attachment having a proximal
end configured to electrically couple to a processor.
22. The method of claim 21, further comprising manufacturing the
second comb structure by forming conductive vias in a
non-conductive substrate.
23. The method of claim 21, further comprising manufacturing the
second comb structure by forming a non-conductive trench in a
conductive substrate.
Description
FIELD
[0001] Embodiments of the subject matter disclosed herein relate to
an ultrasound transducer, and more particularly, to a single
element ultrasound transducer with wafer level back face
attachment.
BACKGROUND
[0002] Single element transducers can be mounted to a distal end of
a probe for invasive imaging of blood vessels or cavities within
the human body. By sending a voltage signal to the two electrodes
of the transducer, a piezoelectric material within the transducer
is excited and generates acoustic signals. The same piezoelectric
material can also convert acoustic signals reflected from an object
into voltage signals. The transducer may be assembled to a cable to
form a forward looking probe, that is, a probe for imaging in the
same direction as the longitudinal axis of the cable. The forward
looking probe can be used in applications such as rectal imaging.
Alternatively, the transducer may be assembled to a cable to form a
side looking probe. By rotating the side looking probe along its
longitudinal axis, a plane perpendicular to the longitudinal axis
of the probe can imaged. The side looking probe can be used in
applications such as intravascular imaging. Multiple single element
transducers may also be assembled into a sparse array (such as a
basket type array) for applications such as mapping a heart
chamber. Since the ultrasound probes are designed for invasive
imaging, miniaturized ultrasound transducers may be utilized.
[0003] Wiring the two electrodes of the transducer to the cable can
be challenging due to the small size of the transducer. One
approach is to attach one electrode of the transducer to a
substrate having a printed circuit, and manually apply silver epoxy
to connect the other electrode to the substrate. However, this
process lacks reproducibility and robustness. Since silver epoxy
has high viscosity, it is difficult to manually apply a controlled
amount of epoxy. Silver epoxy also lacks robust adhesion to the
substrate due to its high sensitivity to moisture and long curing
time. Further, due to long touch time and cycle time, the process
is not suitable for manufacturing disposable probes.
BRIEF DESCRIPTION
[0004] In one embodiment, an ultrasound transducer comprises a
front face, a back face parallel to the front face, and a flex
attachment. The back face includes a signal pad, a ground pad, and
a groove separating the signal pad from the ground pad. The flex
attachment has a first conductive layer and a second conductive
layer separated by a non-conductive layer. The first conductive
layer of the flex attachment is electrically coupled to the signal
pad and the second conductive layer of the flex attachment is
electrically coupled to the ground pad. In this way, the two
electrodes (the ground pad and the signal pad) of the transducer
are integrated into the transducer body with wafer level packaging,
and the transducer may be reliably coupled to the probe via the
flex attachment. Further, such configuration enables fast and
automatic coupling of the transducer with the cable of the
probe.
[0005] It should be understood that the brief description above is
provided to introduce in simplified form a selection of concepts
that are further described in the detailed description. It is not
meant to identify key or essential features of the claimed subject
matter, the scope of which is defined uniquely by the claims that
follow the detailed description. Furthermore, the claimed subject
matter is not limited to implementations that solve any
disadvantages noted above or in any part of this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The present invention will be better understood from reading
the following description of non-limiting embodiments, with
reference to the attached drawings, wherein below:
[0007] FIG. 1 shows an example ultrasound system attached to a
probe including a single element ultrasound transducer.
[0008] FIG. 2A shows a layered substrate.
[0009] FIG. 2B shows a first comb structure made with the layered
substrate.
[0010] FIG. 2C shows a non-conductive base package.
[0011] FIG. 2D shows one embodiment of a second comb structure.
[0012] FIG. 3 shows a three dimensional rendering of the second
comb structure of FIG. 2D.
[0013] FIG. 4 illustrates a procedure for laminating the first and
second comb structures of FIGS. 2B and 2D into an acoustic
stack.
[0014] FIG. 5A shows lateral dicing lines for cutting the acoustic
stack of FIG. 4 into individual single element ultrasound
transducers.
[0015] FIG. 5B illustrates lateral and diagonal dicing lines for
cutting the acoustic stack of FIG. 4 into individual single element
ultrasound transducers.
[0016] FIG. 6A shows a cross-sectional view of a first embodiment
of a transducer.
[0017] FIG. 6B shows a back surface of the transducer of FIG.
6A.
[0018] FIG. 6C shows a three dimensional rendering of the
transducer of FIG. 6A.
[0019] FIG. 7A shows a substrate with conductive base package.
[0020] FIG. 7B shows another embodiment of a second comb
structure.
[0021] FIG. 8 shows the procedure of manufacturing an acoustic
stack based on the second comb structure of FIG. 7B.
[0022] FIG. 9 shows lateral dicing lines for manufacturing a second
embodiment of a transducer.
[0023] FIG. 10A shows a cross-sectional view of a second embodiment
of the transducer.
[0024] FIG. 10B shows a back surface of the transducer of FIG.
9A.
[0025] FIG. 11A illustrates the transducer of FIG. 6A mounted to a
flex attachment for a forward looking probe.
[0026] FIG. 11B illustrates a cross-sectional view of the
transducer of FIG. 6A with the flex attachment mounted to a back
face of the transducer.
[0027] FIG. 11C illustrates the transducer of FIG. 6A surface
mounted to a flex pad for a side looking probe.
[0028] FIG. 12A is a side view of the transducer of FIG. 6A
attached to the flex attachment.
[0029] FIG. 12B is a top view of the transducer of FIG. 6A attached
to the flex attachment.
[0030] FIG. 13 shows a flow chart for manufacturing a transducer
assembly.
DETAILED DESCRIPTION
[0031] The following description relates to various embodiments of
a single element transducer. In particular, systems and methods are
provided for a single element ultrasound transducer with a wafer
level back face attachment for constructing a forward looking or
side looking ultrasound probe. FIG. 1 shows an example
configuration of the forward looking probe within an ultrasound
imaging system. The single element ultrasound transducer is
manufactured through wafer level packaging, by dicing through an
acoustic stack including interdigitated first comb structure and a
second comb structure. Two embodiments of the transducer are
presented. The two embodiments of the transducer are manufactured
with the same first comb structure, but different second comb
structures. In the first embodiment, the second comb structure
includes a non-conductive base package and conductive vias. In the
second embodiment, the second comb structure includes a conductive
base package and non-conductive trench. FIGS. 2A-2D illustrate an
example procedure of manufacturing the first and the second comb
structures with non-conductive base package. FIG. 3 shows a three
dimensional rendering of the second comb structure. FIG. 4 shows
the procedure of assembling an acoustic stack based on the first
comb structure and the second comb structure with non-conductive
base package. Individual transducers may be made by dicing the
acoustic stack. FIGS. 5A-5B show an example dicing pattern for a
first embodiment of the transducer. The structure of the first
embodiment of the transducer is show in FIGS. 6A-6C. FIGS. 7A-7B
show another embodiment of the second comb structure with a
conductive base package and non-conductive trenches. A procedure
for assembling the first comb structure to the second comb
structure with conductive base package is shown in FIG. 8. The
second embodiment of the transducer may be made by dicing the
acoustic stack following lateral dicing lines shown in FIG. 9. The
second embodiment of the transducer, which is a negative to the
first embodiment, is shown in FIGS. 10A-10B. Both the first and the
second embodiments of the transducer have a groove in the back face
of the transducer. The groove can receive a distal end of a flex
attachment as shown in FIGS. 11A-11B for a forward looking probe.
The first and the second embodiments of the transducer may also be
surface mounted to a flat flex pad for a side looking probe as
shown in FIG. 11C. The proximal end of the flex attachment of FIGS.
11A-11B may couple to a coaxial cable as shown in FIGS. 12A-12B.
FIG. 13 is a high level flow chart showing the method of
manufacturing the transducer assembly with wafer level back face
attachment.
[0032] Though a probe with a single element transducer is described
by way of example, it should be understood that the present
techniques may also be useful for constructing a probe with an
array of forward looking single element transducers.
[0033] FIG. 1 is a schematic diagram of an ultrasound imaging
system 100 in accordance with an embodiment of the invention.
System 100 includes a display module 101, a controller/processor
102, a pulser/receiver 103, and a probe 140. The dash lines (110,
120, and 130) indicate communication of electrical signals between
system components. A single element ultrasound transducer 105 is
mounted at one distal end of cable 104. The transducer 105 faces
forward. In other words, the transducer generates and receives
reflected acoustic signals in the same direction as the
longitudinal axis 107 of the probe. The cable 104 may be a coaxial
cable. In an example, the central axis of the coaxial cable may
align with the longitudinal axis 107 of the probe. Probe 140
further includes a sheet 106 covering the cable 104 and the
transducer 105. The sheet may be flexible and transparent to
acoustic signals.
[0034] Pulser/receiver 103 is controlled by the
controller/processor 102 for generating a high voltage pulse to
probe 140. Reflected acoustic signals from an imaged object to the
probe are converted into electrical signals and transmitted back to
the pulser/receiver via 130. The pulser/receiver may amplify the
received electrical signals from the probe. The amplified received
electrical signals are further transmitted to controller/processor
102 via dashed line 120. An image or map of the imaged object is
constructed based on the received electrical signals. The image or
map may be sent to display 101 via dashed line 110 and/or stored in
a memory.
[0035] In another embodiment, the probe may include an array of
ultrasound transducers, and can image or sense a plane or a
volume.
[0036] FIGS. 2A-2D show a first comb structure and one embodiment
of a second comb structure. Each comb structure includes fins and
kerfs that are complimentary to each other. The two comb structures
may be interdigitally laminated together to form an acoustic stack.
In the figures, arrow 261 denotes a horizontal direction. Arrow 263
denotes a vertical direction, perpendicular to the horizontal
direction. The lateral direction 262 is perpendicular to both the
horizontal and vertical directions.
[0037] FIG. 2A shows a cross-sectional view of a layered substrate
210 including a backing layer 211, a matching layer 213, and a
piezoelectric layer 212 intermediate the backing layer and the
matching layer. The backing layer, piezoelectric layer, and the
matching layer are stacked vertically. The layers may be laminated
together using epoxy glue or equivalent.
[0038] The piezoelectric layer may be made with a piezoelectric
material, such as lead zirconate titanate or any other
piezoelectric single crystal. The thickness of the piezoelectric
layer may be half of the wavelength of the acoustic signal. The top
surface and the bottom surface of the piezoelectric layer act as
two electrodes. By applying a voltage across the two electrodes,
the piezoelectric material is excited and generates acoustic
signals in a direction parallel to the vertical direction. The
piezoelectric material may also convert acoustic signals back into
electrical signals. When the piezoelectric material is switched
from the transmission to the receiving mode, a ringing effect may
occur and affect the received signal. The backing layer can dampen
the ringing effect. The backing layer may be made of conductive
material such as graphite, porous graphite filled with resin, or
aluminum. As another example, the thickness of the backing layer
may depend on the required acoustic attenuation. In another
embodiment, a dematching layer may be positioned between the
piezoelectric layer and the backing layer. The dematching layer may
be made of tungsten carbide. In yet another embodiment, the backing
layer may be replaced with the dematching layer. The matching layer
is for matching the acoustic impedance difference between the
transducer and the medium that the transducer is immersed within
during imaging. As an example, the matching layer may be configured
to match the acoustic impedance difference between the transducer
and water when the transducer is used for biological tissue
imaging. The matching layer may be made of conductive material such
as graphite, porous graphite filled with resin, stainless steel, or
aluminum.
[0039] FIG. 2B shows a cross-sectional view of the first comb
structure 220. The first comb structure may be made by dicing the
layered substrate 210. For example, the first comb structure 220
may be manufactured by dicing evenly spaced kerfs (214, 226, and
228) into the layered substrate 210. The kerfs are of the same
dimensions. The kerfs extend along the lateral direction, and are
evenly spaced along the horizontal direction. For example, kerf 214
extends vertically through the backing layer 211 and the
piezoelectric layer 212. Kerf 214 further extends into, but not
through the matching layer 213. As such, fins (215, 225, 227, and
229) are formed. For example, fin 215 includes the backing layer
211, the piezoelectric layer 212, and part of the matching layer
213. The adjacent fins 215 and 225 are separated by a kerf 214.
[0040] FIG. 2C shows a non-conductive base package 230. The base
package may be made by creating evenly spaced kerfs (217, 236, 238,
and 251) along the horizontal axis of a flat non-conductive
substrate. The kerfs are of the same dimensions. For example, the
substrate may be made with aluminum oxide (A1.sub.2O.sub.3)
ceramic, polychlorinated biphenyl (PCB), or silicon. The
non-conductive base package includes fins (216, 235, 237, and 239)
extending laterally. Two adjacent fins, such as fin 217 and fin
235, are separated by a kerf, such as kerf 217. As an example, the
base package is complimentary to the first comb structure in a way
that the height 218 of fin 216 in the base package is the same as
the height 219 of fin 215 in the first comb structure, and the
width 232 of fin 215 in the first comb structure is less than the
width 233 of kerf 217 in the base package. In other words, the
respective height of the fins are the same in both the first comb
structure and the base package and the respective width of the fins
in the first comb structure are less than the respective width of
the kerfs in the base package.
[0041] FIG. 2D shows a cross-section of a second comb structure
240, which is formed from the base package 230. The second comb
structure has fins (246, 271, 273, and 275) and kerfs (247, 272,
274, and 276) complimentary to the fins and kerfs of the first comb
structure 220. The second comb structure has vertically conductive
vias. The second comb structure may be made by drilling a plurality
of first vias (241, 278, 280, and 282) and a plurality of second
vias (242, 279, 281, and 283) vertically through the non-conductive
base package 230, and filling the vias with conductive material
such as tungsten or copper. In one embodiment, the non-conductive
base package is made of Al.sub.2O.sub.3, while the conductive vias
are filled with tungsten. In another embodiment, the non-conductive
base package is made of PCB or silicon, and the conductive vias are
filled with copper. For example, first via 241 is drilled through
fin 216 of the non-conductive base package, from the top surface
231 of fin 216 to the bottom surface 270 of base package 230. The
second via 242 is drilled through the bottom surface 234 of kerf
217 to the bottom surface 270 of base package 230. As such, the
second comb structure includes alternating first and second vias
along the horizontal axis. The entirety of the depth of each of the
vias is filled with the conductive material. In other words, in the
second comb structure 240, the filling for the first via 241 has a
top surface within the same plane of the top surface 248 of fin
246; and the filling for second via 242 has a top surface within
the same plane of the bottom surface 249 of kerf 247. In this way,
the second comb structure 240 and the first comb structure 220 can
be laminated together into an acoustic stack with interdigitated
kerfs and fins.
[0042] Herein, a top surface of a layer refers to a flat surface
extending horizontally and laterally, and is higher than a bottom
surface, wherein the increased height in the vertical direction is
indicated by arrow 263. The side of a layer refers to a side
surface of the layer parallel to the vertical axis.
[0043] FIG. 3 shows a three dimensional rendering of the second
comb structure 240. As shown in FIG. 3, the vias (e.g., vias 241
and 242) are cylindrical in shape, with a round top surface.
However, other via shapes are possible, such as rectangular, oval,
etc. The first conductive via 241 is embedded within the fin 246.
The top surface of the second conductive via 242 is at the bottom
of kerf 247, surrounded by the non-conductive base package 245.
Both fin 246 and kerf 247 extend laterally along the entirety of
the second comb structure.
[0044] FIG. 4 illustrates a procedure of constructing an acoustic
stack from the first and second comb structures. Arrow 261 denotes
a horizontal direction. Arrow 263 denotes a vertical direction,
perpendicular to the horizontal direction. The lateral direction
262 is perpendicular to both the horizontal and vertical
directions. Axis 450 indicates time. The time increases as
indicated by the arrow.
[0045] At T1, the first comb structure 220 is laminated with the
second comb structure 240 to form a laminated stack 410.
Specifically, the fins of the first comb structure are inserted
into the kerfs of the second comb structure, and fins of the second
comb structure are inserted into the kerfs of the first comb
structure. The two comb structures may be bonded by applying glue
in between. As an example, the glue may be non-conducting glue such
as epoxy. As another example, the glue may include an anisotropic
conductive paste in the vertical direction separating the base
package from the matching layer, piezoelectric layer, and the
backing layer.
[0046] At T2, the laminated stack 410 is ground into ground stack
420. Specifically, the top surface of the laminated stack 410 is
ground so that part of the matching layer is removed. As an
example, in the ground stack 420, the thickness of the matching
layer 213 may be one fourth of the wavelength of the acoustic
signal. The matching layer 213 is of the same width in the
horizontal direction and same depth in the lateral direction as the
piezoelectric layer 212 and the backing layer 211. As such, the top
surface of the first via 241 is part of the top surface of ground
stack 420. The first via 241 is separated from the piezoelectric
layer 212 by base package 245. In another embodiment, the bottom
surface of the laminated stack 410 may also be ground to remove
part of the base package, in order to adjust the thickness of the
transducer to a desired thickness.
[0047] At T3, the top surface and the bottom surface of the ground
stack 420 are plated with a first conductive coating 431 and a
second conductive coating 432, respectively. The coating may be
copper, gold, or any type of metal deposition, Further, a second
matching layer 433 is deposited on top of the first conductive
coating 431. As an example, the second matching layer may be chosen
in order to optimize acoustic energy transmission. The second
matching layer may have acoustic impedance between 1.5 and 4MRayl.
The second matching layer may be electrically conductive or
non-conductive.
[0048] At T4, an acoustic stack 440 is made by dicing grooves at
the bottom of the coated stack 430 with a dicing saw, for example.
As shown, groove 441 extends laterally and cuts through the second
conductive coating 432, and into but not through the base package
245. Each groove separates a respective first via and second via,
such as groove 441 separating first via 241 and second via 242.
Each groove is separated from the backing layer 211 by the
non-conductive base package 245.
[0049] FIGS. 5A and 5B show example patterns for dicing the
acoustic stack 440 into individual hexagonal single element
transducers. The acoustic stack 440 may be cut along lateral dicing
and diagonal dicing lines. FIG. 5A shows an example first lateral
dicing line 501 and an example second lateral dicing line 502 in
the cross-sectional view of the acoustic stack 440. The first
dicing line 501 extends vertically along the first via 241,
separating the first via into two parts. The distance 503 between
the first dicing line 501 and the second dicing line 502 along the
horizontal direction is large enough so that part or all of the
second via 242 is within the transducer between dicing line 501 and
502. As another example, the second via 242 and the second dicing
line 502 are separated by the base package 245. As yet another
example, the second dicing line 502 may be along the side surface
505 of a layered stack 429. The layered stack includes the matching
layer 213, the piezoelectric layer 212, and the backing layer 211.
FIG. 5B shows example diagonal dicing lines, such as line 504, as
well as the lateral dicing lines 501 and 502 in a three dimensional
rendering of acoustic stack 440.
[0050] In another embodiment, transducers of other shapes may be
diced out of the acoustic stack. For example, the acoustic stack
may be diced along lateral and horizontal, instead of diagonal,
dicing lines into rectangular transducers.
[0051] FIGS. 6A-6C show different views of a hexagonal single
element ultrasound transducer 600 diced from the acoustic stack 440
as shown in FIGS. 5A-5B. The transducer includes a groove at the
back face of the transducer. The groove separates a ground pad and
a signal pad of the transducer. A flex attachment may be inserted
to the groove for coupling the transducer to a coaxial cable.
[0052] FIG. 6A is a cross-sectional view of transducer 600. The
transducer includes a layered stack 614 comprising a matching layer
601, a piezoelectric layer 602, and a backing layer 603. The
layered stack 614 is separated from a first conductive via 604 by a
non-conductive base package 611. The bottom surface of the backing
layer 603 is in contact with a second conductive via 613. The top
surface of the first conductive via 604, the top surface of the
non-conductive base package 611, and the top surface of the
matching layer 601 define a front surface of the transducer. A
first conductive coating 605 is plated onto the front surface of
the transducer. The first conductive coating 605 is between the
front surface of the transducer and a second matching layer 607.
The second matching layer 607 forms the front face 640 of the
transducer. The groove 608 is embedded within the non-conductive
base package 611. The bottom surface of the first conductive via
604, the bottom surface of the non-conductive base package 611, and
the bottom surface of the second conductive via 613 define a back
surface of the transducer. A second conductive coating (such as 432
in FIG. 4) is applied over the back surface. The second conductive
coating forms a signal pad 609 and a ground pad 606 separated by
groove 608. The bottom surfaces of the ground pad 606 and the
signal pad 609 define a back face 630 of the transducer. The back
face of the transducer is parallel with the front face of the
transducer. The signal pad 609 is in direct contact with the bottom
surface of the first via 604. The ground pad 606 is in direct
contact with the bottom surface of the second via 613. The first
conductive via 604 extends vertically from the signal pad 609 to
the first conductive coating 605. The second conductive via 613
extends vertically from the ground pad 606 to the bottom surface of
the backing layer 603. As such, the transducer is one solid piece
with the signal pad and the ground pad integrated to its body.
[0053] The ground pad 606 is electrically coupled with one
electrode of the piezoelectric layer 602 via the second conductive
via 613 and the backing layer 603. The signal pad 609 is
electrically coupled with the other electrode of the piezoelectric
layer 602 via the first conductive via 604, the first conductive
coating 605, and the matching layer 601. To generate an acoustic
signal, a voltage potential may be applied to the transducer by
electrically coupling a positive tab of a power source to the
signal pad, and a negative (or ground) tab of the power source to
the ground pad of the transducer. Alternatively, a voltage
potential may be applied to the transducer by electrically coupling
a positive tab of the power source to the ground pad of the
transducer, and the negative tab (or ground) tab of the power
source to the signal pad of the transducer. In other words, the
signal and ground pad of the transducer are interchangeable.
[0054] FIG. 6B shows the back surface of the transducer, viewed
along 610 in a direction A-A'. The back surface includes the bottom
surface 620 of the first conductive via 604, the bottom surface
(621a and 621b) of the non-conductive base package 611, the bottom
surface 623 of the second conductive via 613, and groove 608. The
back surface of the transducer is in hexagon shape. The groove 608
separates the bottom surface of the non-conductive base package in
two parts 621a and 621b, each part including a bottom surface of
one conductive via.
[0055] FIG. 6C is a three dimensional rendering of the hexagonal
transducer 600. The non-conductive base package 611 partially
surrounds the first matching layer 601, piezoelectric layer 602,
and the backing layer 603. The first conductive via 604 extends
vertically. The front surface of the transducer is formed by the
top surfaces of first conductive via 604, the base package 611, and
the matching layer 601. The first conductive coating 605 is between
the front surface of the transducer and the second matching layer
607. The groove 608 separates the signal pad 609 and the ground pad
606 of the back face of the transducer.
[0056] FIGS. 7A-7B show a second embodiment for a second comb
structure of the ultrasound transducer. The second comb structure
includes a conductive base package with non-conductive
trenches.
[0057] FIG. 7A is a cross-sectional view of a substrate 710 with
non-conductive trenches evenly spaced along the horizontal
direction. The substrate 710 may be manufactured by dicing trenches
through a conductive base package 711, filling the trenches
entirely with non-conductive material, and grinding the top and
bottom surface of the substrate. As such, the top surface of the
trench 712 is within the same plane as the top surface of the base
package 711. The bottom surface of trench 712 is within the same
plane as the bottom surface of the base package 711. In one
embodiment, the non-conductive trench may be non-conductive resin
such as epoxy glue, and the base package may be graphite.
[0058] FIG. 7B shows a second comb structure 720 with conductive
base package 721. The second comb structure 720 may be made by
dicing substrate 710 to form evenly spaced kerfs (723, 728, 731,
and 733). For example, in order to form the kerf 723, part of the
non-conductive trench 712 is removed as well as part of the
conductive base package 711 along the horizontal direction. The
bottom surface 727 of the kerf 723 abuts both the non-conductive
trench 722 and the conductive base package 721. The second comb
structure includes fins (724, 729, 730, and 732) and kerfs
complimentary to the fins and kerfs in first comb structure 220
shown in FIG. 2B. Specifically, the heights of the fins in the
first comb structure are the same as the heights (e.g., height 726)
of the fin in the second comb structure 720. The width (e.g., width
725) of the kerf in the second comb structure 720 are not less than
the width of the fins in the first comb structure.
[0059] FIG. 8 illustrates a procedure for manufacturing an acoustic
stack 880 with the first comb structure 220 and the second comb
structure 720. Arrow 261 denotes a horizontal direction. Arrow 263
denotes a vertical direction, perpendicular to the horizontal
direction. The lateral direction 262 is perpendicular to both the
horizontal and vertical directions. Axis 840 indicates time. The
time increases as indicated by the arrow.
[0060] At T1, the first comb structure 220 is laminated with the
second comb structure 720 to form a laminated stack 860.
Specifically, the fins of the first comb structure are inserted
into the kerfs of the second negative comb structure, and the fins
of the second negative comb structure are inserted into the kerfs
of the first comb structure. The two comb structures may be bonded
by a glue. As an example, the glue may be non-conducting glue such
as epoxy. As another example, the glue may include an anisotropic
conductive paste in the vertical direction separating the base
package from the matching layer, piezoelectric layer, and the
backing layer.
[0061] At T2, the laminated stack 860 is ground into ground stack
870. Specifically, the top surface of the laminated stack 860 is
ground so that the matching layer 213 is of the same width in the
horizontal direction and the same depth in the lateral direction as
the piezoelectric layer 212 and the backing layer 211. As an
example, thickness of the matching layer 213 may be one fourth of
the wavelength of the acoustic signal. As such, the top surface of
the non-conductive trench 722 is part of the top surface of ground
stack 870. The non-conductive trench 722 is in contact with the
side surface of the layered stack including the matching layer 213,
the piezoelectric layer 212, and the backing layer 211. The
non-conductive trench 722 separates the base package 721 from the
piezoelectric layer 212. In another embodiment, the bottom surface
of the laminated stack may also be ground to remove part of the
base package, in order to adjust the thickness of the transducer to
a desired thickness.
[0062] At T3, acoustic stack 880 is made. In an example, a first
conductive coating 802 may be first plated over the top surface of
the ground stack 870, and then a second matching layer 801 is
deposited on top of the first conductive coating. The second
matching layer may be electrically conductive or non-conductive. A
second conductive coating 804 may be plated over the bottom surface
of the ground stack 870. Then, grooves are created by dicing
through the second conductive coating 804 and into the
non-conductive trench 722. An example groove 808 is shown.
[0063] The acoustic stack 880 may be diced into individual
transducers. FIG. 9 shows example lateral dicing lines for dicing
the acoustic stack 880 into individual transducers. As an example,
the acoustic stack 880 is diced in the horizontal direction by a
first dicing line and a second dicing line. For example, a first
dicing line 910 is between the non-conductive trench 722 and the
layered stack 901. The layered stack 901 includes the matching
layer 213, piezoelectric layer 212, and the backing layer 211. A
second dicing line 920 may be along the side surface of the layered
stack 901. The first and second dicing lines are on opposite sides
of the groove 808.
[0064] In one embodiment, the acoustic stack may be diced into
hexagonal transducers with lateral dicing lines 910 and 920, and
diagonal dicing lines (such as 504 of FIG. 5B). In another
embodiment, the acoustic stack may be diced into rectangular
transducers with lateral dicing lines 910 and 920, and horizontal
dicing lines that are perpendicular to the lateral dicing
lines.
[0065] FIGS. 10A-10B show one embodiment of a hexagonal transducer
1000 diced out of acoustic stack 880 of FIG. 9. The transducer 1000
is a negative of transducer 600, e.g., in transducer 600, the base
package is non-conductive and the vias are conductive; in
transducer 1000, the base packages are conductive and the trench is
non-conductive. FIG. 10A is a cross-sectional view of the
transducer. The first matching layer 1001, piezoelectric layer
1002, and the backing layer 1003 form the layered stack 1004. A
non-conductive trench 1008 separates a first conductive base
package 1007 and a second conductive base package 1017. The first
and second conductive base packages are constructed from base
package 721. The bottom surface of the backing layer 1003 is in
contact with the non-conductive trench 1008 and the second
conductive base package 1017. The top surface of the first
conductive base package 1007, the top surface of the non-conductive
trench 1008, and the top surface of the first matching layer 1001
define a front surface of the transducer. A first conductive
coating 1006 is deposited on top of the front surface, intermediate
the front surface and a second matching layer 1005. The top surface
of the second matching layer defines a front face 1050 of the
transducer. The bottom surface of the first conductive base package
1007, the bottom surface of the non-conductive trench 1008, and the
bottom surface of the second conductive base package 1017 define a
back surface 1020 of the transducer. A second conductive coating is
applied to the back surface. A groove 1011 cuts through the second
conductive coating and separates the second conductive coating into
a signal pad 1009 and a ground pad 1010. The bottom surfaces of the
signal pad and the ground pad define a back face 1060 of the
transducer. The back face is parallel to the front face of the
transducer. The groove 1011 also cuts into, but not through, the
non-conductive trench 1008. Details of the back surface 1020 is
shown in FIG. 10B. The signal pad 1009 is in contact with the
bottom surface of the first conductive base package 1007. The
ground pad 1010 is in contact with the bottom surface of the second
conductive base package 1017. The first base package 1007 extends
vertically from the signal pad 1009 to the first conductive coating
1006. The second base package 1017 extends vertically from the
ground pad 1010 to the bottom surface of the backing layer
1003.
[0066] The ground pad 1010 is electrically coupled with the bottom
surface of the piezoelectric layer 1002 via the second conductive
base package 1017 and the backing layer 1003. The signal pad 1009
is electrically coupled with the top surface of the piezoelectric
layer 1002 via the first conductive base package 1007, the first
conductive coating 1006, and the first matching layer 1001. As
such, when a voltage is applied across the signal pad and the
ground pad, the piezoelectric layer 1002 is excited and generates
acoustic signals in a direction from the back face 1060 to the
front face 1050 of the transducer. A flex attachment may be
inserted into the groove 1011 to couple the two electrodes (the
signal and ground pads) of the transducer to a coaxial cable.
[0067] FIG. 10B shows the back surface 1020 of transducer 1000
viewing from line 1030 in direction B-B'. Groove 1011 separates the
bottom surface of the non-conductive trench 1008 into two parts
(1023a and 1023b). The groove 1011 and the bottom surface (1023a
and 1023b) of the non-conductive trench, insulating the bottom
surface 1021 of the first conductive base package 1007 from the
bottom surface 1022 of the second conductive base package 1017. The
signal pad 1009 covers the bottom surface 1021 of the first
conductive base package and the first bottom surface 1023a of the
non-conductive trench. The ground pad 1010 covers the bottom
surface 1022 of the second conductive base package and the second
bottom surface 1023b of the non-conductive trench.
[0068] FIG. 11A illustrates a flex attachment 1101 having a distal
end configured to be inserted into the groove of the single element
ultrasound transducer. As a non-limiting example, the hexagonal
transducer 600 is shown here. The flex attachment is inserted into
the groove as shown by arrow 1100. The flex attachment includes a
non-conductive middle layer 1104 intermediate a first conductive
layer 1102 and a second conductive layer 1103. The non-conductive
middle layer 1104 may be kapton and the first and second conductive
layers may be copper or gold coated copper, at least in one
example. By inserting the flex attachment into the groove, the
signal pad 609 is in contact with the first conductive layer 1102
and the ground pad 606 is in contact with the second conductive
layer 1103. Conductive glue or soldering may be applied to further
bond the signal or ground pad with the respective conductive layer.
The flex attachment may be a flex PCB. Alternatively, the flex
attachment may be of another substrate utilizing surface mounted
attachment, such as ASICs and 3DMID. The other distal end of the
flex attachment 1101 may be electrically coupled to a processor,
such as an imaging system. The other distal end of the flex
attachment may be coupled to the processor through a cable, such as
a coaxial cable as shown in FIG. 12.
[0069] FIG. 11B illustrates a cross-sectional view of the
transducer with flex attachment 1101 mounted to its back face. The
signal pad 609 of the transducer is in contact with the first
conductive layer 1102 of the flex attachment. The ground pad 606 of
the transducer is in contact with the second conductive layer 1103
of the flex attachment. Conductive glue or soldering 1110a and
1110b are applied to ensure the signal pad 609 is electrically
bonded with the first conductive layer 1102 and the ground pad 606
is electrically bonded with the second conductive layer 1103,
respectively.
[0070] FIG. 11C illustrates surface mounting the single element
transducer to a flat flex pad 1121 for a side looking probe. The
flex pad includes circuit printed on one surface of the flex pad.
As an example, the flex pad may be polyimide. The circuit may be
printed on the flex pad with copper. The circuit may include a
signal pad 1123 and a ground pad 1122. The signal pad and the
ground pad are separated by non-conductive groove 1124. As
indicated by arrow 1120, back face 630 of the transducer may be
laminated to the flex pad by aligning the signal pad 609 of the
transducer with the signal pad 1123 of the flex pad, aligning the
ground pad 606 of the transducer with the ground pad 1122 of the
flex pad, and aligning groove 608 of the transducer with the
non-conductive groove 1124 of the flex pad.
[0071] FIGS. 12A and 12B show the proximal end of the flex
attachment 1101 assembled with a coaxial cable 1210. FIG. 12A is a
side view of the assembly, and FIG. 12B is a top view of the same
assembly. The coaxial cable 1210 includes a jacket 1205, a coaxial
ground 1204, and a coaxial signal 1201. The coaxial ground may be
insulated from the coaxial signal with a dielectric insulator 1207.
The coaxial signal 1201 is bonded to the first conductive layer
1102 of the flex attachment with soldering 1202. Conductive strip
1105 is attached to the non-conductive middle layer 1104, and is on
the same side of the first conductive layer 1102 relative to the
non-conductive middle layer 1104. The conductive strip may be of
the same material as the conductive layers. The coaxial ground 1204
is bonded with the conductive strip 1105 with soldering 1203. The
conductive strip 1105 is connected with the second conductive layer
1103 by a conductive via 1206 through the non-conductive middle
layer 1104. In this way, the coaxial signal is electrically coupled
with the signal pad of the transducer via the first conductive
layer of the flex attachment; the coaxial ground is electrically
coupled with the ground pad of the transducer via the conductive
strip 1105, the conductive via 1206, and the second conductive
layer 1103 of the flex attachment. Electrical signals may be sent
and received to and from the transducer via the coaxial cable.
[0072] FIG. 13 shows an example method 1300 for manufacturing an
ultrasound transducer assembly with its back face coupled to a
coaxial cable.
[0073] At 1301, a first comb structure is manufactured. The first
comb structure includes fins and kerfs. The first comb structure
may be made by dicing kerfs into a layered substrate including a
piezoelectric layer intermediate a matching layer and a backing
layer. An example of the first comb structure is shown in FIG.
2B.
[0074] At 1302, a second comb structure is manufactured. The second
comb structure includes fins and kerfs complimentary to the first
comb structure. The second comb structure may be made out of a
non-conductive substrate or a conductive substrate. In one
embodiment, a non-conductive base package may be made by dicing
kerfs into a non-conductive substrate. Then, through vias are
drilled into the base package, and filled with conductive material.
An example of the second comb structure with non-conductive base
package is shown in FIG. 2D. In another embodiment, through
trenches may first be cut into a conductive substrate, and filled
with non-conductive material. Then, kerfs are cut into the
substrate to construct the second comb structure with conductive
base package, as shown in FIG. 7B.
[0075] At 1303, an acoustic stack is constructed from the first and
second comb structures. The first and second comb structures are
first laminated together, then ground and plated with conductive
coating on the top and bottom surfaces. Further, grooves are cut
into the bottom surface of the plated substrate with a dicing saw,
for example. The procedures of manufacturing the acoustic stack is
shown in FIG. 4.
[0076] At 1304, the acoustic stack is diced into individual
ultrasound transducers. An example pattern for dicing the acoustic
stack with non-conductive base package is shown in FIGS. 5A-5B.
Another example of dicing lines for dicing the acoustic stack with
conductive base package is shown in FIG. 9.
[0077] At 1305, the distal end of a flex attachment is mounted to
the back face of the transducer. As an example, FIGS. 11A-11B show
a layered flex attachment inserted into the groove of the back face
of a hexagonal transducer for constructing a forward looking probe.
As another example, a side looking probe may be constructed by
surface mounting the back face of a hexagonal transducer onto a
flat flex pad with printed circuit printed on top, as shown in FIG.
11C.
[0078] At 1306, the other end of the flex attachment is coupled to
a cable. For example, FIGS. 12A-12B show an example assembly of the
flex PCB with a coaxial cable.
[0079] A technical effect of a single element ultrasound transducer
with two electrodes integrated into the back end of the transducer
is easy attachment to a cable. Another technical effect of the
transducers disclosed herein is enabling simple assembly of the
transducer with a coaxial cable via a flex attachment including a
non-conducive layer intermediate two conductive coating. Another
technical effect of the transducer with a wafer level back face
attachment is that the electrodes of the transducer may be directly
coupled to a coaxial cable with minimal wiring. Another technical
effect of the disclosure is that the transducer may be
automatically assembled with a coaxial cable, avoiding manually
depositing epoxy. Another technical effect of the disclosure is
that the transducer may function reliably and robustly.
[0080] In one embodiment, an ultrasound transducer comprises a
front face, a back face parallel to the front face, the back face
having a signal pad, a ground pad, and a groove separating the
signal pad from the ground pad, and a piezoelectric layer having a
top surface electrically coupled to the signal pad and a bottom
surface electrically coupled to the ground pad. In a first example
of the embodiment, the ultrasound transducer further comprises a
flex attachment having a first conductive layer and a second
conductive layer separated by a non-conductive layer, the first
conductive layer in contact with the signal pad, the second
conductive layer in contact with the ground pad--the piezoelectric
layer intermediate a matching layer and a backing layer. A second
example of the embodiment optionally includes the first example and
further includes, a first conductive via extending vertically from
the signal pad to a conductive coating over a top surface of the
matching layer, and the signal pad is electrically coupled to the
top surface of the piezoelectric layer through the first conductive
via, the conductive coating, and the matching layer. A third
example of the embodiment optionally includes one or more of the
first and second examples, and further includes a second conductive
via, and the ground pad is electrically coupled to the bottom
surface of the piezoelectric layer through the second conductive
via and the backing layer. A fourth example of the embodiment
optionally includes one or more of the first through third
examples, and further includes, further comprising a non-conductive
base package separating the first conductive via from the second
conductive via. A fifth example of the embodiment optionally
includes one or more of the first through fourth examples, and
further includes, the second conductive via is in cylindrical shape
and is surrounded by the non-conductive base package. A sixth
example of the embodiment optionally includes one or more of the
first through fifth examples, and further includes, a first
conductive base package extending vertically from the signal pad to
a conductive coating over the matching layer, and the signal pad is
electrically coupled to the top surface of the piezoelectric layer
through the first conductive base package, the conductive coating,
and the matching layer. A seventh example of the embodiment
optionally includes one or more of the first through sixth
examples, and further includes, a second conductive base package
extending vertically from the ground pad to the back surface of the
backing layer, and the ground pad is electrically coupled to the
bottom surface of the piezoelectric layer through the second
conductive base package and the backing layer. An eighth example of
the embodiment optionally includes one or more of the first through
seventh examples, and further includes, a non-conductive trench
between the first conductive base package and the second conductive
base package. An ninth example of the embodiment optionally
includes one or more of the first through eighth examples, and
further includes, a flat flex pad with circuit printed on one
surface, wherein the back face of the transducer is laminated on
top of the flex pad.
[0081] In another embodiment, an ultrasound transducer assembly,
comprises a piezoelectric layer including a top surface and a
bottom surface; a signal pad electrically coupled to the top
surface of the piezoelectric layer; and a ground pad electrically
coupled to the bottom surface of the piezoelectric layer, the
signal pad and the ground pad located in the same plane and
separated by a groove, the groove configured to electrically couple
the signal pad and the ground pad to a cable. In a first example of
the embodiment, the groove is configured to couple the signal pad
and ground pad to the cable through a flex attachment having a
distal end and a proximal end, the distal end inserted into the
groove and the proximal end coupled to the cable. A second example
of the embodiment optionally includes the first example and further
includes, the flex attachment has a first conductive layer in
contact with the signal pad and a second conductive layer in
contact with the ground pad, and the first conductive layer is
insulated from the second conductive layer by a non-conductive
layer. A third example of the embodiment optionally includes one or
more of the first and second examples, and further includes, a
backing layer having a top surface in contact with the bottom
surface of the piezoelectric layer; and a matching layer having a
top surface and a bottom surface, the top surface of the matching
layer plated with a conductive coating, the bottom surface of the
matching layer in contact with the top surface of the piezoelectric
layer. A fourth example of the embodiment optionally includes one
or more of the first through third examples, and further includes,
a conductive via extending vertically from the conductive coating
to the signal pad, and a non-conductive base package between the
conductive via and the piezoelectric layer. A fifth example of the
embodiment optionally includes one or more of the first through
fourth examples, and further includes, a first conductive base
package extending vertically from the conductive coating to the
signal pad, and a non-conductive trench between the first
conductive base package and the piezoelectric layer. A sixth
example of the embodiment optionally includes one or more of the
first through fifth examples, and further includes, a second
conductive base package coupled between the backing layer and the
ground pad, the second base package separated from the first base
package by the non-conductive trench.
[0082] In another embodiment, a method comprises laminating a first
comb structure and a second comb structure into an acoustic stack,
the first comb structure having fins including a piezoelectric
layer intermediate a matching layer and a backing layer, the second
comb structure having fins and kerfs; plating a first conductive
layer over a top surface of the acoustic stack; plating a second
conductive layer over a bottom surface of the acoustic stack;
cutting a groove through the second conductive layer; dicing the
cut acoustic stack into an ultrasound transducer having a back face
including a signal pad and a ground pad separated by the groove;
and inserting a distal distal end of a flex attachment into the
groove, the flex attachment having a proximal end configured to
electrically couple to a processor. In a first example of the
embodiment, the method further includes manufacturing the second
comb structure by forming conductive vias in a non-conductive
substrate. A second example of the embodiment optionally includes
the first example and further includes manufacturing the second
comb structure by forming a non-conductive trench in a conductive
substrate.
[0083] As used herein, an element or step recited in the singular
and proceeded with the word "a" or "an" should be understood as not
excluding plural of said elements or steps, unless such exclusion
is explicitly stated. Furthermore, references to "one embodiment"
of the present invention are not intended to be interpreted as
excluding the existence of additional embodiments that also
incorporate the recited features. Moreover, unless explicitly
stated to the contrary, embodiments "comprising," "including," or
"having" an element or a plurality of elements having a particular
property may include additional such elements not having that
property. The terms "including" and "in which" are used as the
plain-language equivalents of the respective terms "comprising" and
"wherein." Moreover, the terms "first," "second," and "third," etc.
are used merely as labels, and are not intended to impose numerical
requirements or a particular positional order on their objects.
[0084] This written description uses examples to disclose the
invention, including the best mode, and also to enable a person of
ordinary skill in the relevant art to practice the invention,
including making and using any devices or systems and performing
any incorporated methods. The patentable scope of the invention is
defined by the claims, and may include other examples that occur to
those of ordinary skill in the art. Such other examples are
intended to be within the scope of the claims if they have
structural elements that do not differ from the literal language of
the claims, or if they include equivalent structural elements with
insubstantial differences from the literal languages of the
claims.
* * * * *